The primary objective of this research is to develop new paradigms of theoretical understanding and experimental measurement of vibration of biological tissue in the low audible frequency range. It is emphasized that this research is not meant to develop new imaging methodologies to compete with ultrasound or other existing methods. Instead, the investigators are proposing a fundamental study of biological tissue vibration that could provide additional information about "function" that may not be accessible by mere "structural" imaging. Understanding tissue vibratory behavior is expected to contribute to the development of entirely new techniques offering high sensitivity and specificity, reduced cost and greater portability. For example, consider the possibility of a hand-held inexpensive device that, in a few seconds using audible sound, could painlessly and accurately diagnose conditions such as a collapsed lung, a perforated gut, or severity of a carotid occlusion. This low audible frequency range is of interest since internal vibratory sources of the cardiovascular, pulmonary, gastrointestinal and musculoskeletal systems are dominated by spectral content below 1 kHz. Additionally, " active" diagnostic methods, such as sonoelastic imaging, externally introduce vibratory energy in the low audible frequency range and measure the resulting tissue response. In order to rationally explore the meaning of the measured complex acoustic signals, it is critical to know the effect that the intervening tissue (for example, skin, fascia, fat) has in modulating the signal between generation and detection. In spite of the wealth of information present in the low-frequency range that can be of great diagnostic value, fundamental aspects of low audible frequency wave vibration in biological tissue are poorly understood. Below a few kHz, both compression, shear, surface and interlayer surface wave propagation can be significant and highly dependent on tissue properties. Recent preliminary research of the PI and members of this team has led to an improved understanding of this vibro- acoustic problem. This study proposes the innovative implementation of theoretical, computational and experimental techniques, currently used in nonbiological vibration genres, to further enhance our understanding of low frequency tissue vibration in a complex biological condition in order to lay the groundwork for the development of new diagnostic methods. It is anticipated that the new theoretical paradigms in tissue vibration coupled with innovative measurement methods could eventually improve the diagnostic capabilities for diseases that would be within the domain of at least six different NIH institutes: NCI, NHLBI, NIA, NIAMS, NIDDK, and NINDS.